In general, in a toner fixing member 1 (e.g., a fixing roll or a fixing belt) used in a copying machine, and the like, a layer 3 comprising an elastic body (e.g., rubber) is formed on a cylindrical substrate 2, and a fluororesin layer 6 (e.g., tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin [PFA] or polytetrafluoroethylene resin [PTFE]) is further formed as the surface layer on the elastic layer 3 via an adhesive layer 7, as shown in FIG. 2.
Various toner fixing members, such as fixing rolls and fixing belts, are proposed. For example, Patent Document 1 proposes a (silicone) rubber-fluororesin laminate formed by bonding a rubber layer, such as silicone based rubber, to the surface of a cylindrical substrate via an adhesive for rubber layer, and further bonding tubular PFA to the rubber layer using an adhesive, such as a silicone based adhesive or an imide based adhesive.
Such a toner fixing member is required to have a thinner fluororesin layer in terms of toner fixing properties; however, there were problems in that the inner surface treatment of thinner tubular fluororesin was difficult, and the adhesion of the thinner tubular fluororesin with an elastic layer was poor.
To address these problems, Patent Documents 2 to 5 propose various silicone rubber-fluororesin laminates, including laminates provided with an undercoat agent layer and/or a primer layer between an elastic body layer and a fluororesin layer.
Patent Document 2 proposes a fixing roller and a fixing belt comprising a substrate, and an elastic layer and a surface layer that are sequentially formed on the substrate, wherein the surface layer is formed by heat shrinkage of a PFA tube, and the surface layer and the elastic layer are bonded together by means of an adhesive material containing 20 to 30 wt % of PFA. The fixing roller and fixing belt are low in cost because the inner surface of the PFA tube is not treated. Further, the fixing roller and fixing belt characteristically have a thin primer layer. The surface roughness is small, and the initial adhesion is excellent; however, the hot adhesion and the adhesion after a long-term heating test are not satisfactory, as shown in Comparative Example 5, provided later.
Patent Document 3 proposes a fixing member obtained by applying primer treatment to an elastic layer formed on a cylindrical or columnar substrate using an epoxy based primer, and the like, further forming a fluororesin layer, completely covering the fluororesin layer with a heat shrinkable tube shrunk by heating, and forming a film by heating and baking. The fixing member has a smooth surface with a surface roughness Rz of 5 μm or less; however, the initial adhesion, the hot adhesion, and the adhesion after a long-term heating test are not satisfactory.
Patent Document 4 discloses a fluorine-containing laminate comprising a substrate, a primer layer formed on the substrate, and a molding layer formed on the primer layer, wherein when silicone rubber is selected as heat resistant rubber that forms the substrate, the primer layer comprises a functional group-containing, fluorine-containing ethylenic polymer containing an alkoxysilane monomer polymer (and an organic titanate compound), and the molding layer is formed from a fluorine-containing resin molded product using a heat shrinkable PFA tube. The fluorine-containing laminate also has low surface roughness and excellent initial adhesion; however, the hot adhesion and the adhesion after a long-term heating test are not satisfactory.
Patent Document 5 proposes a heating roller comprising a silicone rubber coating layer provided on a metal hollow core bar, and a thin film made of PFA as the outermost layer, wherein a primer layer with a two-layer structure is inserted between the silicone rubber coating layer and the PFA thin film, and the primer layer has a lower layer comprising a mixture containing a silicone resin and a silane coupling agent as main components, and an upper layer comprising a mixture containing an alkoxy-modified fluororesin as a main component. The heating roller has a uniform film thickness, and has excellent initial adhesion, as well as satisfactory surface roughness and hot adhesion; however, the adhesion after a long-term heating test is not satisfactory.
As for the adhesion, it is known that the addition of metal oxide (e.g., rouge Fe2O3), which has high activity and many functional groups, to primers can enhance adhesion; however, in some cases, the adhesion is not satisfactory depending on the level of adhesion required for fixing members of copying machines.
Thus, none of these conventionally proposed laminates sufficiently satisfies the hot adhesion and the adhesion after a long-term heating test. This is attributable to the following reason. Silicone rubber and fluororesin are poorly compatible because of their different structures; particularly, there is a tendency in that since reactive functional groups are poor in the vulcanized silicone rubber side, the adhesion of the silicone rubber side is low.
Therefore, even if a fluorine based primer is used, the fluororesin and the primer are bonded together by heat melting; on the contrary, the adhesion with the silicone rubber is reduced. As a result, the fluororesin and the silicone rubber initially seem to be bonded together; however, the adhesion may be reduced in a heated environment, such as a hot state or long-term heating. Furthermore, the surface of the vulcanized silicone rubber is in an inactive state, and low molecular weight components that inhibit adhesion are present on the rubber surface; the adhesion between the primer and the rubber may be deteriorated.